Applicants hereby claims foreign priority benefits under U.S.C. xc2xa7 119 of Japanese Patent Application No. 2002-374327, filed on Dec. 25, 2002, and the content of which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to a fuel injection control device of a diesel engine, and more particularly to a fuel injection control device for executing multiple injection by conducting a plurality of auxiliary injections and a main injection within one cycle.
2. Description of the Related Art
Diesel engines equipped with a fuel injection control device for executing multiple injection (multiinjection) by conducting a plurality of auxiliary injections and a main injection within one cycle have recently been suggested (for example, Japanese Patent Applications Laid-open Nos. 2000-205021 and 2001-50097).
The applicant has invented a fuel injection control device for executing multiple injection, such as shown in FIG. 2. FIG. 2 shows a drive pulse (current pulse) outputted to a drive circuit of injectors for executing fuel injection with the injectors; in the figure, a crank angle is plotted against the abscissa.
In multiple injection, a total of four injections (three types of auxiliary injections and a main injection) are executed within one cycle. First, a pilot injection PI is carried out at the instant of time prior to the main injection M. This is done for premixing the fuel. Then, a pre-injection PR is carried out immediately prior to the main injection M. This is done to produce flame and prevent an ignition delay. Then, the main injection M is carried out in the vicinity of compression top dead center TDC, and an after-injection AF is carried out after the main injection M. This is done to burn the non-combusted fuel.
A post injection is sometimes carried out after the after-injection AF. This is, however, done to improve the treatment capability of an exhaust gas after-treatment device and makes no contribution to the combustion in the engine. Accordingly, this injection will not be considered herein.
The injection quantity of each auxiliary injection is determined based on the parameters representing the engine operation state such as engine revolution speed and engine load. For example, the optimum injection quantity of each auxiliary injection is determined by tests conducted in advance for each operation state, and a respective map is created for each auxiliary injection. Then, the injection quantity for each auxiliary injection is determined from the maps based on the parameters such as engine revolution speed and engine load that were actually detected.
The injection quantity of the main injection is determined as follows.
First, a total injection quantity Qtotal of the fuel injected within one cycle is determined from the map based on the parameters representing the engine operation state such as engine revolution speed and engine load. Further, the injection quantities Qsub of each auxiliary injection are then determined from the above-mentioned maps for auxiliary injections. The injection quantity Qmain of the main injection is then computed by subtracting the sum Qsubtotal of injection quantities Qsub of auxiliary injections from the total injection quantity Qtotal (Qmain=Qtotalxe2x88x92Qsubtotal).
However, in the above-described fuel injection control device there were cases in which the injection quantity Qmain of the main injection decreased below the necessary minimum limit due to engine operation state. In other words, at least a certain fraction (this fraction differs depending on the engine operation state) of the total injection quantity Qtotal had to be secured as the injection quantity Qmain of the main injection, but there were cases in which the fraction taken by the injection quantity Qmain of the main injection in the total injection quantity Qtotal decreased below the lower limit value as a result of subtracting the sum Qsubtotal of injection quantities Qsub of auxiliary injections from the total injection quantity Qtotal.
Furthermore, it was understood that certain engine operation states result in a contradiction in that the sum Qsubtotal of injection quantities Qsub of auxiliary injections becomes larger than the total injection quantity Qtotal of fuel.
For example, such a problem can be encountered when the total injection quantity Qtotal becomes very small, for example in an engine idle mode. One of the reasons is that injection quantity Qsub of each auxiliary injection assumes a minimum value in the region in which the total injection quantity Qtotal is very small. However, because the injection quantity control capabilities of injectors are limited, the injection quantity Qsub of auxiliary injections has to be set at a minimum injection quantity of injectors or higher on the map. For example, if the minimum injection quantity of an injector is 2 mm3/st, setting has to be made to 2 mm3/st even though the optimum injection quantity of auxiliary injection is, for example, 1.6 mm3/st. As a result, the above-described problem sometimes occurs in a region in which the total injection quantity Qtotal is very small.
Furthermore, the injection quantity Qsub of each auxiliary injection is determined from the map and then corrected based on the water temperature and intake temperature, but the above-described problem sometimes occur when the injection quantity Qsub of each auxiliary injection is incrementally corrected.
It is an advantage of the present invention to provide a fuel injection control device for determining the injection quantity of the main injection by subtracting the sum of injection quantities of auxiliary injections from the total injection quantity of fuel, wherein the fraction assumed by the injection quantity of the main injection in the total injection quantity can be secured at least to a minimum limit value necessary for the engine operation state.
In order to attain the above-mentioned object, the present invention provides a fuel injection control device for executing multiple injection by conducting a plurality of auxiliary injections and a main injection within one cycle, comprising first means for determining the total injection quantity Qtotal of fuel injected within one cycle based on the parameters representing the engine operation state; second means for determining base injection quantities QBsub of each of the auxiliary injections based on the parameters representing the engine operation state; and third means which, when the sum QBsubtotal of base injection quantities QBsub of each of the auxiliary injections is not larger than the value obtained by multiplying the total injection quantity Qtotal by a coefficient K (0 less than Kxe2x89xa61), computes the injection quantity QTmain of the main injection by subtracting the sum QBsubtotal from the total injection quantity Qtotal, and when the sum QBsubtotal is larger than the value obtained by multiplying the total injection quantity Qtotal by the coefficient K, computes the injection quantity QTmain of the main injection by reduction correcting the base injection quantities QBsub of the auxiliary injections so that the sum QBsubtotalxe2x80x2 of injection quantities QBsubxe2x80x2 of auxiliary injections after the correction becomes not larger than the value obtained by multiplying the total injection quantity Qtotal by the coefficient K, and subtracting the sum QBsubtotalxe2x80x2 after the correction from the total injection quantity Qtotal. With the fuel injection control device in accordance with the present invention, the injection quantity of the main injection can be secured at least to a minimum limit value necessary for the engine operation state. Furthermore, the occurrence of the aforesaid contradiction relating to computation is prevented.
Here, the third means may compute a correction coefficient C by dividing the value obtained by multiplying the total injection quantity Qtotal by the coefficient K by the sum QBsubtotal when the sum QBsubtotal of base injection quantities QBsub of each of the auxiliary injections is larger than the value obtained by multiplying the total injection quantity Qtotal by the coefficient K, multiply each of the base injection quantities QBsub of auxiliary injections by the correction coefficient C, and reductionally correct the base injection quantities QBsub of each auxiliary injection at equal ratio.
Further, the third means may determine the coefficient K based on parameters representing the engine operation state such as engine revolution speed and engine load.